ciml - 6:38 am on Aug 19, 2011 (gmt 0)
If you're not able to track via telephone numbers with enough granularity and if you're willing to reduce your conversion rate for a while, you could replace the (presumably) site-wide telephone number with a 'contact us now' link. The correlation between visitor to contact page and visitor to lead is often high, when you're looking at keywords.
If you're willing to go a step further, you could optimise the lead form for online leads and then track visitor to sale. This may mean losing a few sales for a while, but the intelligence could be worth more in the longer term if you believe your keywords and bids leave a lot of room for improvement.